JPH02198427A - Liquid crystal space optical modulator and its driving method - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal space optical modulator being small in size and low in cost which can execute a high speed response by inserting and holding a ferroelectric liquid crystal between a first transparent insulating substrate and a second transparent insulating substrate, and connecting a first and a second DC power sources so that a first and a second conductive light shielding films become a reverse bias against a counter electrode, respectively. CONSTITUTION:This optical modulator is provided with a picture element electrode 101, a photoconductive body layer A 102 formed so as to cover an end part of its picture element electrode, and a conductive light shielding film A 103 formed so as to cover the photoconductive body layer without coming into contact with a picture element point. Also, it is structured by inserting and holding a ferroelectric liquid crystal 109 between a glass substrate A 106 formed by providing a photoconductive body layer B 104 formed so as to cover a different end part of the picture element electrode, and a photoconductive light shielding film B 105 for covering the photoconductive body layer B without coming into contact with the picture element electrode 101, and a glass substrate B 108 on which a counter electrode 107 is formed. As for an external electrode, a DC power source A 110 and a DC power source B 111 are connected so that the conductive light shielding films A, B become a negative bias and a positive bias against the counter electrode, respectively. In such a way, the liquid crystal space optical modulator being small in size and low in cost which can execute a high speed response is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a liquid crystal spatial light modulator used for optical information processing and a method for driving the same.

(Prior art) Liquid crystal spatial light modulators can process two-dimensional optical information in parallel and simultaneously, so they can be applied to parallel optical logic elements or image processing elements, and will be an important key in building optical computers in the future. It has the potential to become a device.

FIGS. 6(a) and 6(b) are diagrams showing the structure and equivalent circuit of a conventional liquid crystal spatial light modulator, respectively. The conventional liquid crystal spatial modulator has a transparent electrode A601 as shown in FIG. 6(a).
, a photoconductor layer 602 , a light shielding film 603 , and a reflective film 60
4 is formed on the glass substrate A605, and the transparent electrode B6
A nematic liquid crystal 608 is sandwiched between glass substrates B607 on which 06 is formed, and an AC power source 609 is connected as shown in the figure. Nematic liquid crystal is usually lysted nematic (hereinafter abbreviated as TN).
Mode is adopted and twisted orientation is applied. 6th
In Figure (a), the layer of alignment treatment material for obtaining twisted orientation is omitted. This is because it is not directly involved in the operation of the liquid crystal spatial light modulator.

The equivalent circuit is as shown in FIG. 6(b), in which a resistor 612 of the photoconductor layer and a resistor 613 of the liquid crystal layer are connected in series using an AC power source. The resistance of the photoconductor layer is shown as a variable resistance because its resistance value changes depending on the intensity of input light.

The operating principle and driving method of the liquid crystal spatial light modulator will be explained below.

In FIG. 6, the photoconductor layer resistance 612 when the input light 610 is irradiated and not is shown as the bright resistance Rph, respectively.
Assuming that the dark resistance is Rd and the resistance 613 of the liquid crystal layer is RLC, they are selected so that the following relationship holds between Rph, Rd, and RLC.

Rph<<RLC<< Rd (1) Therefore, when no input light is irradiated, most of the applied voltage supplied from the AC power supply 609 is applied to the photoconductor layer, and no electro-optic effect occurs in the liquid crystal layer. Conversely, when input light is irradiated, the resistance of the photoconductor layer decreases and most of the applied voltage is applied to the liquid crystal layer, causing switching of the liquid crystal. That is, the 0N10FF of the input light can cause the liquid crystal to turn 0N10FF, and an optical input/output system is established.

As shown in FIG. 6(a), input light 610 is transmitted to a glass substrate A.
The output light 611 is read out as light emitted from the side of the glass substrate B and reflected by the reflective film. At this time, the polarizing plate A614 and the polarizing plate B615 installed on both sides of the liquid crystal spatial light modulator are set to either balanced Nicols with the same polarization direction, or crossed niffles with orthogonal polarization directions, and in the former case, the input light Bright TrueLogic (hereinafter referred to as BTL) indicates that the output light is bright when irradiated with
In the latter case, Dark True Logic (hereinafter referred to as DTL) indicates that the output light is dark when the input light is irradiated.
).

It is said that the key element in constructing an optical computer is an optical bistable element. An optical bistable element is an element in an optical input/output system that has two stable states as output light for a certain input state. One example of a more specific optical functional device that has been developed from optical bistable devices is the optical flip-flop device.

An optical flip-flop device can be made using a liquid crystal spatial light modulator. FIG. 7 shows a conventional method for realizing a set/reset (S-R) optical flip-flop device using the liquid crystal spatial light modulator.
D0PTIC8vol, 2. No. 13 (19)
84)pp.

2163). This method uses two liquid crystal spatial light modulators, a liquid crystal spatial light modulator A701 and a liquid crystal spatial light modulator B702. The set optical signal 114 is input to the liquid crystal spatial light modulator A, and the reset optical signal 113 is input to the liquid crystal spatial light modulator B. Part of the output light from the liquid crystal spatial light modulator A is extracted as output light Q711 via the Glanton-Thompson prism 703 and the half mirror 704, and the other part is used as readout light for the liquid crystal spatial light modulator B. .

Liquid crystal spatial light modulator B read out by the readout
The output light of is mirror 705, polarizing plate B709, and mirror C7.
By adding the feedback light to the set optical signal using the optical system No. 07, an S-R optical flip-flop element is realized. This optical flip-flop element can switch the state of the liquid crystal by applying a set optical signal and a reset optical signal in the form of pulses, and can be used directly as an optical storage element.

(Problems to be Solved by the Invention) In the SR optical flip-flop device using the conventional liquid crystal spatial light modulator described above, nematic liquid crystal is used as the liquid crystal material. The electro-optic response time of nematic liquid crystal is several tens to hundreds of m5ec, and the response time of the liquid crystal spatial light modulator is determined by the response time of nematic liquid crystal. In other words, the response time of conventional liquid crystal spatial light modulators is slow, ranging from tens to hundreds of m5ec, and the above problem becomes a major bottleneck in performing optical information processing at higher speeds using liquid crystal spatial light modulators. There is.

Furthermore, in the conventional method for realizing an optical flip-flop using a liquid crystal spatial light modulator, two liquid crystal spatial light modulators are required, and a method is adopted in which the output light Q is fed back to the set optical signal. In addition to requiring two liquid crystal spatial light modulators, this method also requires two devices for optical feedback.
It requires one Glan Thompson prism, one half mirror, and three mirrors, and a space to install them.
Requires space to secure a feedback optical path. This is a factor that increases the size of the device and increases the manufacturing cost.

Ferroelectric chiral smect liquid crystals respond faster to electric fields than nematic liquid crystals. That is, while nematic liquid crystal has a response time of several tens to hundreds of m5ec, ferroelectric liquid crystal exhibits a high-speed response of several tens to several hundred psec, which is two to three orders of magnitude faster. Therefore, if a ferroelectric liquid crystal is used as the liquid crystal material of a liquid crystal spatial light modulator, it is possible to realize a high-speed liquid crystal spatial light modulator that responds in tens to hundreds of psec. Furthermore, in addition to its high-speed characteristics, ferroelectric liquid crystals also have the characteristic of electro-optic bistability, and by utilizing this effect, it is possible to create an S-R optical flip-flop device that does not require an optical feedback system. can do.

However, while the TN liquid crystal switches with an electric field of 0N10FF, the ferroelectric liquid crystal switches with inversion, so the structure of the conventional liquid crystal spatial light modulator cannot switch the ferroelectric liquid crystal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a small, low-cost liquid crystal spatial light modulator capable of high-speed response, which eliminates the above-mentioned problems of the prior art, and a method for driving the same.

(Means for Solving the Problems) The liquid crystal spatial light modulator of the present invention includes one or more pixel electrodes, and first and second photoconductor layers respectively formed at different ends of the pixel electrodes. and first and second conductive light-shielding films formed to respectively cover the first and second photoconductor layers without contacting the pixel electrodes; , a ferroelectric liquid crystal is sandwiched between a second transparent insulating substrate on which a counter electrode is formed, and the first and second conductive light shielding films are each reversely biased with respect to the counter electrode. It is characterized in that first and second DC power sources are connected.

Further, one or more pixel electrodes, first and second photoconductor layers formed respectively at different ends of the pixel electrodes, and the first and second photoconductor layers formed without contacting the pixel electrodes,
a first transparent insulating substrate comprising first and second conductive light-shielding films each formed to cover the photoconductor layer;
A ferroelectric liquid crystal is sandwiched between a second transparent insulating substrate on which a counter electrode is formed, and the first and second conductive light-shielding films are arranged to have a reverse bias with respect to the counter electrode. 1. In a method for driving a liquid crystal spatial light modulator connected to a second DC power source, one of the first and second photoconductor layers,
A set optical pulse signal is input from the second transparent insulating substrate side, and the second
This is a method for driving a liquid crystal spatial light modulator, characterized in that a reset light pulse signal is input from the transparent insulating substrate side of the first transparent insulating substrate, and reading light is emitted from the first transparent insulating substrate side.

(Function) The liquid crystal spatial light modulator of the present invention has a structure in which the potential of the pixel electrode is reversed when a set optical signal is input and when a reset optical signal is input, when the counter electrode is used as a reference. Therefore, the switching of the ferroelectric liquid crystal can be controlled using a set optical signal and a reset optical signal. Furthermore, when neither the set optical signal nor the reset optical signal is input, the potential of the pixel electrode is Ov, and since the ferroelectric liquid crystal has electro-optic bistability, the set optical signal and the reset optical signal The state at the time of input can be retained.

Therefore, it is possible to realize a high-speed SR optical flip-flop element using a liquid crystal spatial light modulator, and it is possible to process optical information at higher speed. Furthermore, the S-R optical flip-flop element can not only be realized with only one liquid crystal spatial light modulator, but also does not require an optical feedback system. It is also possible to reduce the size and cost of the optical flip-flop element.

(Example) Examples of the present invention will be described in detail below.

(Example 1) FIG. 1 is a diagram showing an example of the liquid crystal spatial light modulator of the present invention. FIG. 1(a) shows the cross-sectional structure of the liquid crystal spatial light modulator. In this embodiment, the number of pixels is one. A pixel electrode 101, a photoconductor layer AlO2 formed to cover an end of the pixel electrode, and a conductive light-shielding film AlO3 formed to cover the photoconductor layer A without contacting the pixel points. , a photoconductor layer B104 formed to cover an end different from the end of the pixel electrode, and a conductive light-shielding film B105 so as to cover the photoconductor layer B without contacting the pixel electrode. Glass substrate A106,
It has a structure in which a ferroelectric liquid crystal 109 is sandwiched between a glass substrate B108 on which a counter electrode 107 is formed. The external power source is a DC power source A110 so that the conductive light shielding films A and B have a negative bias and a positive bias, respectively, with respect to the counter electrode.
and a DC power supply B111 are connected.

In order to impart electro-optic bistability to the ferroelectric liquid crystal, the cell gap is controlled to about 1.5 pm by the spacer 112.

Here, a plan view and a sectional view of a glass substrate A on which a photoconductor layer, which can be said to be the heart of the liquid crystal spatial light modulator of the present invention, is formed are shown in FIGS. 2(a) and 2(b), respectively.

In this embodiment, the photoconductor layer AlO2 and the photoconductor layer B104 are formed at a corner portion that shares one side of the pixel electrode 101, and the conductive light shielding film AlO3 and the conductive light shielding film B105 are They are formed to cover the photoconductor layer A and the photoconductor layer B, respectively. Note that the photoconductor layer AlO2 and the photoconductor layer B104 may be formed diagonally, as long as the two layers do not overlap.

A cross-sectional view of the glass substrate A106 taken along line AB is shown in FIG. a-8 as the photoconductor material
i: H was adopted. The reason why a-8i:H was adopted is that the a-8i:H material exhibits high-speed response as a photoconductor material and has high sensitivity in the visible light region. High sensitivity in the visible light range means that liquid crystal spatial light modulators can process visible images. As the photoconductor layer, zinc sulfide (ZnS), zinc oxide (Zn
It is also possible to use O), cadmium sulfide (CdS), and selenium (Se).

Photoconductor layers A and B are pixel electrodes and conductive light-shielding films A,
In order to make ohmic contact with B, the n+ layer 2o1-R
A three-layer structure of 202-n+ layer 203 was used, and Cr2O4 was used as the conductive light-shielding film, but A1 may also be used. Furthermore, the photoconductor layers A1 and B formed on the glass substrate A are fabricated symmetrically with respect to the center line 205 in FIG. 2(b), and both exhibit exactly the same photoconductive properties.

FIG. 1(b) is a diagram showing an equivalent circuit of the liquid crystal spatial light modulator of the present invention. Resistor 119 of photoconductor layer A and resistor 120 of photoconductor layer B each receive a reset optical signal 113.
, and 0N10FF of the set optical signal 114, the resistance value changes, so it is shown as a variable resistor. It is also known that the liquid crystal layer is represented by a parallel connection of a resistor 121 and a capacitor 122, which are connected between contacts A and B as shown in FIG. 1(b).

The operating principle of the liquid crystal spatial light modulator of the present invention is shown below in Figure 1 (
This will be explained using the equivalent circuit of b).

Resistance of liquid crystal layer RLC-reset optical signal to photoconductor layer A
Rpha is the resistance of photoconductor layer A when irradiated to The resistance of photoconductor layer B when not irradiated is Rphb, and the resistance of photoconductor layer B when not irradiated is Rd.
b, it is assumed that the film thickness and impurity concentration of each layer are selected so that the following relationship holds.

Rpha:Rphb<<RLC<<Rda:Rdb(2
) Also, the voltages of DC power supply A and DC power supply B are equal vB
shall be.

Below, under the above conditions, the ferroelectric liquid crystal layer will be examined in three states: when the set optical signal is irradiated, when the reset signal is irradiated, and when neither the set optical signal nor the reset optical signal is irradiated. Find the voltage applied to.

(a) When the set light signal is irradiated When the set light signal is irradiated onto the photoconductor layer B, the voltage applied to the liquid crystal layer is based on A, and the equivalent circuit (
2) From the formula, +■Bv is obtained.

(b) When the reset light signal is irradiated When the reset light signal is irradiated onto the photoconductor layer A, the voltage applied to the liquid crystal layer is based on the point A, based on the above equivalent circuit and equation (2). , -vBv.

(C) When neither the set optical signal nor the reset optical signal is irradiated When neither the set optical signal nor the reset optical signal is irradiated, the voltage applied to the liquid crystal layer is calculated from the above equivalent circuit and equation (2) as OV becomes.

Therefore, the electric field applied to the liquid crystal layer can be switched between positive and negative by the set optical signal and the reset optical signal, and it is possible to drive the ferroelectric liquid crystal that causes switching by reversing the electric field.

Based on the above operating principle, in FIG. 1(a), a reset optical signal 113 is irradiated from the glass substrate A side to the photoconductor layer A, and a set optical signal 114 is irradiated from the glass substrate A side to the photoconductor layer B. However, if the readout light 115 is passed through the polarizing plate A 117, the liquid crystal spatial light modulator, and the polarizing plate B 118 in this order, and is used as output light, an optical output controlled by the set optical signal and the reset optical signal can be obtained. At this time, polarizing plates A and B are installed on both sides of the liquid crystal spatial light modulator.
is set to crossed nicols.

Next, a method for driving the liquid crystal spatial light modulator of this embodiment will be explained below with reference to FIGS. 3 and 4.

FIGS. 3(a) to 3(d) are diagrams illustrating the optical input/output characteristics of the liquid crystal spatial light modulator of this embodiment. Figures (a) and (b), and (C) and (d) respectively show the cases of the BTI and DTL described above, and this shows the polarizing plate A and the polarizing plate set to crossed Nicols. They can be mutually converted by rotating B by the tilt angle of the ferroelectric liquid crystal, 45 degrees.

In Fig. 3(a), the x-y plane and the x-y plane are on the same plane and show the dependence of the liquid crystal applied voltage on the set/reset light intensity, and the y-z plane shows the dependence of the liquid crystal applied voltage on the output light intensity. Indicates dependence.

In the x-y plane, for an increase in the set optical signal intensity,
The voltage applied to the liquid crystal changes almost linearly from Ov to +■Bv. Further, in the fy plane, the voltage applied to the liquid crystal changes almost linearly from 0 to -vBv as the reset optical signal intensity increases. On the other hand, in the liquid crystal spatial light modulator of this embodiment, since the ferroelectric liquid crystal exhibits electro-optic bistability, the electro-optic characteristics of the liquid crystal are as shown in the yz plane.

From the three-dimensional coordinates shown in Figure 3(a) above, if the x-z plane and x-z plane are expressed on the same plane and the set/reset optical input/output characteristics are determined, as shown in Figure 3(b). When both the set optical signal and reset optical signal are not irradiated,
A kind of optical bistable state is realized in which the output light has two stable states.

In the case of DTL, the optical input/output characteristics shown in FIG. 3(d) can be similarly obtained from the three-dimensional coordinates shown in FIG. 3(e).

FIG. 4 is a diagram showing the optical response characteristics of the liquid crystal spatial modulator of this embodiment, which shows the set/reset optical input/output characteristics shown in FIGS. 3(b) and 3(d).

In this example, both the set optical signal and the reset optical signal are cut off outside the set time and outside the set time, and the voltage applied to the liquid crystal is 0 during that time, and the ferroelectric liquid crystal with electro-optic bistability retains its previous state. During the set time, a set optical signal as shown in FIG. 4(a) is inputted to the photoconductor layer B from the glass substrate A side in FIG. 1(a). Even after the set light pulse is turned off, the output light remains in the set state for a period of T1 until the next reset light pulse is input, as shown in FIG. 4(C).

During the reset time, a reset optical signal as shown in FIG. 4(b) is inputted to the photoconductor layer A from the glass substrate A side in FIG. 1(a). Even after the reset light pulse is turned off, the output light maintains the reset state for a period T2 until the next set light pulse is input, as shown in FIG. 4(C).

On the other hand, in the case of DTL, the set of Figures 4(a) and (b)
When a reset optical signal is input, an optical response is obtained as shown in FIG. 4(d), which is an inversion of the output light of FIG. 4(C).

As described above, in the liquid crystal spatial light modulator of this example,
The set/reset light input/output characteristic exhibits optical bistability, and the state of the output light can be switched by the set light pulse and the reset light pulse by the driving method described above. Further, a light pulse width of 200 psec is sufficient to switch the ferroelectric liquid crystal, and high-speed operation can be achieved. In addition, BTL,
The fact that DTL can be easily obtained by simply rotating two polarizing plates by 45 degrees is a very advantageous point when applying the present liquid crystal spatial light modulator to an optical logic element.

(Embodiment 2) FIGS. 5(a) and 5(b) are diagrams showing an embodiment of the liquid crystal spatial light modulator of the present invention. In the first embodiment, the number of pixels is 1, but this embodiment shows an example in which the number of pixels is 16 (4×4) pixels.

FIG. 5(a) shows the pixel electrode 101 and the photoconductor layer AlO2.
A glass substrate A106 on which a photoconductor layer B104, a conductive light-shielding film AlO3, and a conductive light-shielding film B105 are formed.
FIG. Also, Figure 5(b)
is an enlarged view of the vicinity of a pixel electrode, and also shows a photoconductor layer A and a photoconductor layer B formed under conductive light-shielding films A and B, respectively.

In FIG. 5(a), the conductive light-shielding film A formed at the upper left corner of the pixel electrode so as to cover the photoconductor layer A is connected to the connection terminal A301, and the photoconductor layer A is formed at the lower left corner of the pixel electrode. A conductive light-shielding film B formed to cover the body layer B is connected to a connection terminal B502. Furthermore, the connection terminal A and the connection terminal B are connected in the bias direction shown in FIG. 5(a) via the counter electrode and a DC power supply A110 and a DC power supply B111, respectively.

Further, in FIG. 5(B), a cross-sectional view when the glass substrate A is cut along line segment AB is the same as FIG. 2(b) in Example 1.

In this embodiment, each pixel is independently
This is represented by the equivalent circuit shown in Figure (b), and therefore each pixel can be driven independently. In other words, this embodiment has better parallel processing ability than the first embodiment.

(Effects of the Invention) As explained above, by applying the liquid crystal spatial light modulator of the present invention, an S-R optical flip-flop consisting of only one liquid crystal spatial light modulator that does not require optical feedback can be created. It can be realized. This eliminates the need for optical components such as Glan-Thompson prisms and mirrors that were required in conventional optical feedback systems, and also eliminates the space in the feedback optical path.Furthermore, it eliminates one liquid crystal spatial light modulator. Since it is possible to miniaturize the S-R optical flip-flop device using a liquid crystal spatial light modulator,
Cost reduction can be achieved.

Furthermore, the liquid crystal spatial light modulator of the present invention has a response speed two to three orders of magnitude faster than that of a free liquid crystal spatial light modulator, making it possible to perform faster optical information processing.

[Brief explanation of the drawing]

1(a), (b) and 2(a), (b) are schematic diagrams of a liquid crystal spatial light modulator according to Example 1 of the present invention, and FIG. 3(a)
~(d), Figures 4(a) to (d) are diagrams showing the driving method of Example 1 of the present invention, and Figures 5(a) and (b) are liquid crystal spatial light modulation of Example 2 of the present invention. Schematic diagram of the vessel, Figures 6(a) and (b)
) is a schematic diagram of a conventional liquid crystal spatial light modulator, and FIG. 7 is a schematic diagram of an S-R optical flip-flop element using a conventional liquid crystal spatial light modulator. In the figure, 101... pixel electrode, 102... photoconductor layer A, 103... conductive light shielding film A, 104...
- Photoconductor layer B, 105... Conductive light shielding film B, 10
6...Glass substrate A, 107...Counter electrode, 10
8... Glass substrate B, 109... Ferroelectric liquid crystal, 1
10...DC power supply A, 111...DC power supply B, 11
3... Reset optical signal, 114... Set optical signal,
115...Reading light, 116...Output light, 117
...Polarizing plate A, 118...Polarizing plate B, 601...
Transparent electrode A, 602... Photoconductor layer, 603... Light shielding film, 604... Reflective film, 605... Glass substrate A
, 606...Transparent electrode B, 607...Glass substrate B
, 608... Nematic liquid crystal, 609... AC power supply, 610... Input light, 611... Output light, 61
4...Polarizing plate A, 615...Polarizing plate B, 701...
・Liquid crystal spatial light modulator A, 702...Liquid crystal spatial modulator B
, 703...Glan Thompson Prism, 704...
・・Half mirror-1705・Mirror A, 706・
...Mirror B, 707...Mirror C, 708...Polarizing plate A, 709...Polarizing plate B, 710...Output light Q, 711...Output light Q.

Claims (2)

[Claims] (1) One or more pixel electrodes, first and second photoconductor layers formed respectively at different ends of the pixel electrodes, and the first and second photoconductor layers formed without contacting the pixel electrodes.
a first transparent insulating substrate comprising first and second conductive light-shielding films each formed to cover the photoconductor layer;
A ferroelectric liquid crystal is sandwiched between a second transparent insulating substrate on which a counter electrode is formed, and the first and second conductive light-shielding films are arranged to have a reverse bias with respect to the counter electrode. 1. A liquid crystal spatial light modulator characterized in that a second DC power source is connected. (2) one or more pixel electrodes, first and second photoconductor layers formed respectively at different ends of the pixel electrodes, and the first and second photoconductor layers formed without contacting the pixel electrodes;
a first transparent insulating substrate comprising first and second conductive light-shielding films each formed to cover the photoconductor layer;
a second transparent insulating substrate on which a counter electrode is formed; In a method for driving a liquid crystal spatial light modulator connected to a second DC power source, inputting a set optical pulse signal to one of the first and second photoconductor layers from the second transparent insulating substrate side;
A reset light pulse signal is inputted to the other of the first and second photoconductor layers from the second transparent insulating substrate side, and reading light is irradiated from the first transparent insulating substrate side. A method for driving a liquid crystal spatial light modulator.